Two tops, A and B have equal rotational inertias. They spin on a table. Initiall

Question

Two tops, A and B have equal rotational inertias. They spin on a table. Initially top A has angular velocity 20 rad/s pointing downward, top B anugular velocity 30 rad/s pointing upward. a) (5 points) If the rotational kinetic energy of top A is initially 6.0 J, find its rotational inertia. _________________ b) (5 points) The tops bump into one another and separate. After the collision top B has angular velocity 15 rad/s pointing downward. Find the change in the angular momentum of top B. ___________________ c) (5 points) Find the angular velocity of top A after the collision. _____________________ d) (5 points) If the tops were in contact for 2.0 ms (millisecond), find the magnitude of the average torque on top B during the collision. ________________________

Explanation / Answer

KE=0.5I2

6*2/400=I

I=0.03kg.m2

Conservation of Angular momentum

I.20-I.30=I.15+Ia

a=-10/15=-0.66rad/s or 0.66rad/s pointing upward

change in angular momentum of b=0.03.(15+30)=0.135 units

Average torque =0.135/0.002=67.5 N.m

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